<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>固定的底栏</title>
  <style>
    * {
      /*margin: 0;*/
    }
    .Site {
      display: flex;
      min-height: 100vh;
      flex-direction: column;
    }
    header,footer {
      height: 100px;
      flex:1;
      background-color: #ddd;
      text-align: center;
      align-content: center;
      border-radius: 20px 20px 0 0;
    }
    footer {
      border-radius: 0 0 20px 20px;
    }
    .Site-content {
      flex: 12;
      background-color: pink;
    }
  </style>
</head>
<body>
 <div class="Site">
   <header>固定底边栏(页头)</header>
   <main class="Site-content">内容</main>
   <footer>固定底边栏(页尾)</footer>
 </div>

</body>
</html>
